Process for sensitizing articles for metallization and resulting articles

ABSTRACT

Surfaces of articles are sensitized for the deposition of adherent metal from electroless metal solutions in contact therewith by prior treatment with an activatable complex of copper in a liquid medium formed from a solution comprising a mixture of halogen, cuprous and cupric components and thereafter forming a deposit on the treated article surfaces of a water-insoluble derivative of the said complex. Such surface deposits are treated with a reducing agent or water to enhance their reception of metal in an electroless metal deposition bath.

This application is a continuation of application Ser. No. 796,809,filed May 13, 1977, now U.S. Pat. No. 4,199,623, as a continuation ofapplication Ser. No. 520,355, filed Nov. 1, 1974, now abandoned, inturn, a continuation-in-part of application Ser. No. 407,555 filed Oct.18, 1973 and application Ser. No. 270,861, filed July 11, 1972.

This invention relates to processes for pre-sensitizing and sensitizingarticles to the deposition of metals from solutions thereof andresultant articles. More particularly, it relates to improved means forproviding adherent metal layers on articles by treating the surface ofsuch articles so as to form catalytically active elements or precursorsof same for contact with electroless metal deposition solutions.

Sensitizing substrates to the deposition of electroless metal, e.g.,Group IB and VIII metals, i.e., copper, cobalt, nickel, gold, silver,and the like, is a key step in the production of decorative andindustrially useful metallized objects, such as name plates, dials,printed circuits, and the like. This sensitization is conventionallycarried out by treating the substrate either stepwise with a solution ofstannous tin or similar ions, followed by contacting with a solutioncontaining precious metal ions, such as palladium or platinum, or all inone step with a unitary colloidal suspension of precious metal or with asoluble complex of precious metal ion, stannous ion and an anion. Theseprocesses yield a sensitive surface which when immersed in aconventional electroless metal deosition bath causes metal to deposit onall of the sensitized areas thereof.

A number of proposals have been made to carry out such processes moreeconomically and efficiently:

Chiecchi, U.S. Pat. No. 3,379,556 discloses immersion in abeta-resorcylato chromic chloride solution to eliminate pretreatmentssuch as sealing, sandblasting, etching, and the like. This method stillrequires the use of a two-step, stannous-palladium subsequent treatment.See, for example, Schneble et al, U.S. Pat. Nos. 3,403,035 and3,033,703. Moreover, the chromium complexes are difficult to prepare,stabilize and use. In addition, the complex must be polymerized afterapplication and before subsequent treatment steps.

Bernhardt et al, U.S. Pat. No. 3,547,784, disclose treating anon-metallic surface with stannous salt then with a silver salt and thenelectrolessly plating using processes and deposition baths for copper,nickel and silver found, for example, in Schneble et al, U.S. Pat. Nos.3,527,215 and 3,347,724. The Bernhardt et al process is conventional andthe point of novelty resides in using a particular copolymer of vinylchloride which was not easy to metallize up until the time of theinvention.

In a more recent development, there have been provided so-called metalreduction sensitizers, which can employ base metal ions, followed bytreatment with reducing solutions or radiant energy, e.g., heat, light,and the like, to produce the sensitized surface.

The metal reduction sensitizing process consists of coating a surface,preferably one which has been activated in known ways to render itpermanently polarized and wettable, or microporous, with a reduciblemetal salt solution, e.g., CuSO₄.5H₂ O, NiSO₄.6H₂ O, and the like, theneither draining, semi-drying or completely drying the so-treatedsurface. Sensitization is then completed by immersing the surface in astrongly reducing medium, e.g., a sodium borohydride solution, duringwhich step the metal salts are reduced to elemental metal particles.This sensitized surface is then rinsed and electrolessly plated.

Due to the solubility of these reducible metal salts, surfaces contactedtherewith cannot be rinsed without removing all of the salts from thesurface. And when the surfaces are not rinsed, the drag-over of excessmetal salts into the reducing medium shortens its life and turns itblack with atomic metal particles.

If a means could be provided to rinse excess and unwanted metal saltsfrom the surface before immersion in the reducing medium, theabove-noted problems would be avoided. In addition, control would befacilitated because rinsing would provide a positive indication that theonly remaining materials are those elemental particles which areadsorbed by the surface and which are necessary for subsequent catalyticactivity.

"Inorganic Reactions And Structures" by Edwin S. Gould, Henry Holt &Co., New York, N.Y., 1955, at page 165, mentions transient phenomenawherein the reduction of copper (II) halides to copper (I) halides maybe carried out by means of copper metal in a concentrated hydrochloricacid solution, with the liquid taking on an "intermediate black color"before fading to the colorless CuCl₂ ⁻ ion. Gould theorizes that theblack color is probably due to dimeric or polymeric ions having copperin both the +1 and +2 states, e.g., [Cl-Cu-Cl-CuCl₂ (H₂ O)]⁻. Thispublication does not disclose or suggest any utility for Gould'sunstable material, any manner of stabilizing it, or any definitequantitative relation of Cu⁺ and Cu⁺⁺ for yielding same.

According to the present invention, improvements are disclosed forrendering surfaces sensitive to electroless metal deposition. Thedisclosed sensitizing process uses copper and its compounds and yetyields results comparable to the use of conventional, expensive, andsomewhat unstable sensitizers based entirely on precious metals.

In comparison with the prior art techniques, the instant system providesthe following distinct advantages:

(i) more complete rinsing of the treated substrate can now be toleratedbecause of tremendously improved adsorption of the copper complex in theseeder medium on the substrate surface and insolubilization thereon;

(ii) the "take" or coverage in the electroless metal bath is whollyuniform and rapid; and

(iii) in the case of activated substrates, metallization within thesurface micropores is deep and complete, thereby enhancing strength ofthe bond between deposited metal and substrate.

According to the present invention, there are provided processes forpre-sensitizing and sensitizing surfaces of articles for the subsequentdeposition of adherent metal from an electroless metal depositionsolution in contact therewith, said processes including the step oftreating the surface or selected areas of the surface of said articlewith a liquid seeder medium comprising an activatable complex containingcopper, thereby adsorbing said complex on said surface in situ. Theadsorbed copper-containing complex is then rendered water-insoluble.

Certain embodiments of the novel processes also involve treating thewater-insoluble derivative with one or more activating agents such asreducing agents or water, either simultaneously with or subsequent tothe insolubilization step, to enhance the conversion of the deposit intoa state which is more active to the deposition of electroless metal.

Still other process modifications relate to a process combinationwherein such treatments are followed by an electroless metal depositionstep.

Other aspects of the invention as well as its nature, objects andadvantages will be apparent to those skilled in the art uponconsideration of the detailed disclosure hereinafter.

The present method involves pre-sensitizing a substrate surface byadsorption thereon of a copper-containing complex in a liquid seedermedium. The adsorbed material is then rendered into a water-insolubledeposit on that surface.

Sensitizing liquid media according to the invention may be formed by,for example, admixing a polar liquid such as water, a source of copper,such as copper salt, elemental copper, copper oxide, and the like, ormixtures thereof, a source of halogen, and, optionally and preferably, asource of hydrogen ions.

Although the active seeding components resulting from initially formingsolutions according to this disclosure are herein designated as"complexes," and we believe that they are in fact complexes, their exactnature and composition is unclear. Specific references to thesecharacteristics are included as out best collective judgement as to whatactually occurs, and results, when the procedures we describe arepracticed.

In the process, liquid seeders formed from solutions according to theinvention are believed to include an activatable copper complex. Theactivatable complex of copper in a liquid medium is brought intointimate contact with a substrate, preferably by immersion in the mediumfor a period which may be exemplified as about 5 to 10 minutes at roomtemperature or elevated temperatures. This activatable complex often hasan essentially dark or even black appearance and is formed from asolution including moieties of copper in both its +1 and +2 valencestates. The complex may be of a polymeric nature. The composition of theliquid seeder forming solutions is described in detail hereinafter, andit appears that the complex formed therefrom is strongly adsorbed on thesubstrate surface.

The actual composition of complexes according to the invention is notknown. As further described below, useful complexes are obtained byforming solutions comprising a halogen component, a cuprous componentand a cupric component. It is believed that complexes according to theinvention contain at least two copper atoms, and that these atoms haveat least two different oxidation numbers selected from the groupconsisting of 0, 1 and 2. It is further believed that these complexescontain at least one halogen atom. As also described in greater detailinfra, solutions yielding copper-containing complexes according to theinvention preferably contain cuprous/cupric copper atoms in the weightratio of at least 0.4 to 1.

The above-described complex is then rendered into a water-insolublederivative. The preferred method is to expose the treated substrate,while it is still wet with the sensitizing liquid, to a quantity of anaqueous medium sufficient to precipitate the adsorbed material as awater-insoluble derivative of the complex and also to wash off anyexcess solution that was not adsorbed on the surfaces of the substrate.This deposit is in the form of an adherent layer on the surfaces of thesubstrate that were exposed to the seeder solution. Itsinsolubilization, or precipitation as a water-insoluble derivative ofthe said copper complex in this fashion, is believed to be the result ofa hydrolysis reaction.

If, for example, the insolubilization agent comprises water or dilutesulfuric acid, the initial precipitate formed on the treated surfaceduring the water treatment is believed to include copper salts, andindeed may consist essentially of copper salts. At the point at whichthe sensitizer-treated surface first is provided with an insolubledeposit; the surface may be considered to be pre-sensitized andessentially not yet catalytic to electroless metal deposition. We sayessentially because, as described in detail below, we are dealing with acontinuum of relative catalytic activity which, although generallycontrollable, prohibits flat statements with respect to the existence ofno catalytic activity whatever.

In any event, if insolubilization of the copper complex is accomplishedvia treatment of the substrate with water, and this water treatment ishalted immediately upon the formation of an adherent precipitate coatingon the substrate, a pre-sensitized substrate results. The article maythen be dried and stored for later sensitization as described infra,which may be followed by metallization in electroless metal depositionbaths, or it may be immediately further processed.

If, rather than halting water-treatment upon the formation of theadherent pre-sensitizing material, one continues the water treatment,the substrate is transformed over a continuum from a pre-sensitizedsubstrate to a sensitized substrate that is catalytic to electrolessmetal deposition. We believe this result to be attributable to thedisproportionation of copper atoms having oxidation numbers other thanzero to form copper atoms in the elemental state, i.e., having anoxidation number of zero, and the resultant formation of microcatalyticsites on the substrate surface. This change from pre-sensitized surfaceto sensitized surface may be observed on a macro scale after aboutone-half to a full minute's treatment with water, since it is usuallyaccompanied by the pre-sensitized surface turning green as it assumes asensitized or catalytically-active state.

Alternatively, the pre-sensitized substrate may be reduced to render itsensitized, for example by treating with a reducing agent followinginsolubilization.

Whether the sensitization of the pre-sensitized substrate isaccomplished via disproportionation or reduction, the sensitized articlemay be set aside and stored for later adherent metallization inelectroless metal deposition processes.

Still another alternative to the above-described sensitization processis to catalyze the pre-sensitized substrate in the electroless metaldeposition bath, for example by incorporating a suitable reducing agenttherein. Practice of this method avoids the requirement of conducting aseparate and distinct catalyzing step in the process while stillenabling ultimate catalyzation and electroless metal deposition.

The present seeder compositions comprise liquid media containingactivatable complexes prepared from solutions containing both monovalentand divalent copper. With aqueous media, the complex-containing liquidsare generally dark to black, with amber hues apparent at lowerconcentrations (e.g., a total dissolved Cu content of about 20 grams perliter or less). The quantity of dissolved copper in these solutions isnot critical, and it may range from a barely effective concentration tolarge proportions that are restricted only by solubility characteristicsor economic considerations. For illustration, the total dissolved coppercontent of the solutions may range from about 0.5 to 30% by weight ormore, and concentrations of about 5 to 15% are preferred.

The atomic ratio (weight ratio) of monovalent copper to divalent copperin the original solution is significant, as better yields and depositsof the complex are obtainable with an increase in that ratio, at leastin the lower part of the range which may extend from about 0.4:1 to aratio of 30:1 or more. Ratios of about 0.7:1 to about 20:1 appear to bebetter for general use. The Cu⁺ :Cu⁺⁺ ratio may be adjusted to thechosen value by a number of methods to be described.

Other components may desirably be present in these sensitizingcompositions, such as stabilizers and wetting agents.

The stabilizers preserve or stabilize the liquid seeder during routineuse or storage over an extended period. Such stabilizers includeelemental metals, such as cobalt, iron, aluminum, nickel and copper,which aid in maintaining desirable oxidation number ratios andequilibria among the various components. Amines and halides are alsouseful stabilizers. Such substances as hydrochloric acid and sodium orpotassium chloride tend to prevent excessive oxidation of the monovalentcopper component, particularly when elemental copper is also present.Generally, a large excess of halogen seems to be beneficial, and inaddition to being provided as above, useful halogens may be provided byhydrofluoric, hydrobromic and hydriodic acids and their soluble salts.Other useful stabilizers include resorcinol and barium and cobalthalides, such as the chlorides.

For prolonged storage, it is recommended that the pH of the solution bemaintained at about 3.5 or below with HCl or another halogen containingacid.

The liquid seeders of the present invention may be prepared by severaldifferent methods which are described in detail in the examples.Broadly, the preparatory methods encompass mixing or otherwisecontacting, continuously or intermittently, starting materials thatcontain copper atoms having at least two different oxidation numbersuntil the said complex is formed. For the present purposes, thoseoxidation numbers include the zero state of uncombined copper metal aswell as monovalent and divalent copper moieties.

One method involves oxidizing a cuprous compound (e.g., cuprouschloride) in an excess of a halogen acid (e.g., hydrochloric acid) untilthere is sufficient divalent copper for the formation of the liquidseeder medium.

A second process involves reducing some cupric halide in a halogen acidwith metallic cobalt, nickel, iron, aluminum or copper present,preferably in the absence of air, until there is enough monovalentcopper for formation of the liquid seeder or sensitizer.

A third preparatory method that is often preferred for better control ofthe ratio of monovalent copper to divalent copper is to add both cuprousand cupric components to a strong solution of a halogen acid in water

In all three processes, the appearance of a black or dark amber color inthe liquid usually indicates that the activatable complex of copper hasbeen formed. The existence of useful concentrations of a complex inliquids according to the invention can be tested by the formation, uponcontacting with, or addition to, water, of a precipitate. Thepreparation of the seeder liquids is usually carried out at roomtemperature but heating above about 40° C., and especially boiling, cansubstantially improve the stability of the seeder liquid in certaininstances.

Preferably, the seeder medium also contains a surfactant or wettingagent which will seek and affix itself firmly to the surface beingtreated, e.g., by electrical attraction or other means. Preferably also,that medium or the next treating liquid comprises a wetting agent havinga polarity which is opposite to the polarity of at least some of thesurface sites of the article to be sensitized. Fluorinated hydrocarbonsare the preferred wetting agents.

In a preferred feature of the process of this invention, the enhancingagent or agents following pre-sensitization may be reducing agents, suchas borohydrides, amine boranes, hydrazine hydrate, formaldehyde andothers. It has been found that alkali metal borohydride compositions areespecially useful and may be stabilized by proper attention to pH. Ifthe pH of an aqueous sodium borohydride solution, which is normallyabout 9.4 (this and other pH values herein are measured at 25° C.), isadjusted upward, e.g., to 12-12.7, by adding a pH adjustor, e.g., analkali metal hydroxide, i.e., sodium hydroxide, or phosphate and thelike, any tendency to decompose is minimized and the working life isextended remarkably. However, pH's of above about 13 should be avoided,because there is a tendency to reduce the desired enhancementcharacteristics. Enhancement occurs at a pH of below 9.4, but thenstability of the borohydride solution tends to be impaired.

In one embodiment, a precursor of a sensitizing medium may be formedwhen a copper compound or mixture thereof is mixed with ammonia or amineto form a copper complex with ammonia or amine or a mixture thereof, andthe desired proportions of monovalent and divalent copper areestablished as described hereinbefore. Not only are ammonia or amines intheir own rights powerful wetting agents, but so are the formed ioncomplexes. It appears that these ion complexes behave much likequaternary ammonium complexes, e.g., cationically. Such positivelycharged (polar) ion complexes are adsorbed by negative surface sites onthe article to be sensitized. However, the complexes of copper formedfrom halogen-containing solutions are usually preferred, e.g., thoseprepared with an excess of hydrochloric acid or a chloride salt.

The present invention may be used to sensitize a wide variety ofsubstrates, including non-metallic, insulating substrates and metallicsubstrates.

Non-metallic substrates include glass, porcelain, cloth, paper,compressed wood, and resins, both thermoplastic and thermosetting, andmixtures thereof.

Among the thermoplastic resins may be mentioned the acetal resins;acrylics, such as methyl acrylate; cellulosic resins, such as ethylcellulose, cellulose acetate, cellulose propionate, cellulose acetatebutyrate, cellulose nitrate and the like; chlorinated polyethers; nylon;polyethylene; polypropylene; polystyrene; styrene blends, such asacrylonitrile styrene copolymer and acrylonitrile-butadiene-styrenecopolymers; polycarbonates; polyphenyloxide; polysulfones;polychlorotrifluoroethylene; and vinyl polymers and copolymers, such asvinyl acetate, vinyl alcohol, vinyl butyral, vinyl chloride, vinylchlorideacetate copolymer, vinylidene chloride and vinyl formal.

Among the thermosetting resins may be mentioned allyl phthalate; furane;melamine-formaldehyde; phenol formaldehyde and phenol-furfuralcopolymer, alone or compounded with butadiene acrylonitrile copolymer oracrylonitrile-butadiene-styrene copolymers; polyacrylic esters;silicones; urea formaldehydes; epoxy resins; allyl resins; glycerylphthalates and polyesters.

A preferred embodiment includes the use of a substrate having a surfacemade up of an adherent resinous layer, the layer having uniformlydispersed therein finely divided particles of oxidizable and degradablesynthetic or natural rubber. Such bases are disclosed in U.S. Pat. No.3,625,758.

The sensitization of metallic substrates is also possible with liquidseeder media according to the invention. Those skilled in the art areaware that it is sometimes desirable to catalyze elemental metalsurfaces in order to build up further adherent metal deposits thereon inelectroless metal deposition baths. Catalytic sites provided bysubstrates sensitized according to the invention may be useful inattaining such built-up metallization areas, whether the plating metalbe the same or different than the original metal substrate.

One way to activate resinous bases is to render them permanently polarand wettable by treatment first with a preactivating agent, such as astrong organic solvent like dimethyl formamide, dimethyl sulfoxide,methyl ethyl ketone or a mixture of toluene and water, and so forth,depending on the nature of the resin, then with an activator such aschromic acid-sulfuric acid, and then with a reducing agent, such assodium bisulfite or hydroxylamine hydrochloride, the result of which isto produce a permanently polarized, wettable surface.

Such techniques are disclosed in greater detail, for example, incopending U.S. patent application Ser. No. 227,678, filed Feb. 18, 1972,the disclosure of which is incorporated herein by reference.

On the other hand, the surface of the resinous article can be partiallydegradable, or be provided with a surface layer having such properties,or contain degradable particles, such as rubber particles, and ontreatment with suitable agents, such as chromic acid or permanganate, becaused to become microporous and thus activated to adherent metaldeposits. See, e.g., U.S. Pat. No. 3,625,758 to Stahl et al.

Any conventional electroless metal deposition bath useful withconventional precious metal sensitized surfaces can be used to depositmetal on the surfaces sensitized according to this invention. Generally,the deposition baths will contain an ion of the metal or metals whosedeposition is desired, (e.g., copper, nickel, cobalt, silver, gold, andthe like), a complexing agent for the ion, a reducing agent for the ionand an agent to adjust the bath to an optimum, predetermined pH. Suchbaths are amply described in the patent and textbook literature.

The following examples illustrate various forms of the invention.

EXAMPLE 1

The following redox mixture is prepared:

CuCl₂.2H₂ O: 60 g.

CuCl: 35 g.

*Hydrochloric acid: 200 ml.

Water sufficient for: 1 liter

Copper metal sheet: 500 cm.²

The atomic or weight ratio of monovalent to divalent copper in thecompounds charged here is 1:1 and the mixture is agitated in thepresence of the copper metal in sheet form until the liquid becomes darkin a relatively short time, which is normally an indication of theformation ofa copper-containing complex which can be activated forcatalyzing electroless deposition of metals.

EXAMPLE 2

An analogous redox composition is prepared using chemically equivalentquantities of cupric bromide, cuprous bromide and hydrobromic acid inplace of the corresponding chlorine compounds in the formulation ofExample 1. Agitation of this mixture also produces a complex of copperwhich can be activated as described herein for catalyzing electrolessmetal deposition.

EXAMPLE 3

Another redox formulation is compounded like that of Example 1 withchemically equivalent quantities of cupric iodide, cuprous iodide andhydriodic acid substituted for the corresponding chlorine compounds.Again, agitation of this mixture produces a complex that is adaptablefor activation for catalyzing the deposition of metals by theelectroless metal technique.

EXAMPLE 4

Still another composition analogous to that of Example 1 is mixed withchemically equivalent amounts of cupric fluoride, cuprous fluoride andhydrofluoric acid in lieu of the chlorine derivatives. Stirring thisformulation produces a complex similar to that of Example 1 and isactivatable for catalyzing substrates in a like manner.

EXAMPLE 5

Another redox formulation is prepared by heating the followingcomposition to 40° C. with agitation until it becomes black.

CuCl: 100 g.

CuCl₂.2H₂ O: 100 g.

HCl: 500 ml.

3-M surfactant FC-98: 0.5 g.

Water sufficient for: 1 liter

Copper metal sheet: 500 cm.²

The atomic ratio of monovalent copper to divalent copper in thematerials charged here is 1.72:1.

EXAMPLE 6

A different type of redox sensitizing solution is prepared according tothetabulation immediately hereinafter with resorcinol added as astabilizing agent and with potassium chloride serving to provide thehalogen.

CuCl: 50 g.

CuCl₂.2H₂ O: 5 g.

Potassium Chloride: 100 g.

Resorcinol: 50 g.

Surfactant FC-98: 0.5 g.

Water sufficient for: 1 liter

The order of adding these ingredients is of no significance. The atomicratio of monovalent copper to divalent copper introduced into thiscomposition is 17.2:1, much higher than before. Following development ofadark copper complex composition upon heating somewhat above 40° C., thecomposition is tested by adding a few drops to water and also byimmersing a glass slide first in the treating composition and thereafterin water. In both instances, a precipitate is formed which is indicativeof an activatable complex of copper. After three days of storage, thesetwo tests are repeated with the same results thereby indicating that thetreating composition has good storage stability. For considerably longerstorage, it may be desirable to add enough hydrochloric acid to reducethepH of the treating composition to 3.5 or lower.

EXAMPLE 7

A further embodiment of the resorcinol-stabilized seeder composition oftheredox type is prepared by boiling the following components togetherfor a relatively short time in forming the desired complex.

CuCl: 80 g.

CuCl₂.2H₂ O: 200 g.

Resorcinol: 100 g.

HCl: 500 ml.

Surfactant FC-98: 0.5 g.

Water sufficient for: 1 liter

The atomic ratio of the monovalent copper to divalent copper in thestarting material of this composition is 0.69:1. This formulation isboiled during its preparation in order to eliminate an observed tendencyto precipitate on cooling. Such heating also improves the storagestability of the composition over a period of at least three days bymaintaining its efficiency as a seeding composition substantially higherthan is possible with a corresponding composition that is not boiled.Other trials indicate that when the resorcinol is omitted from theformulation of this example, the resulting complex loses itseffectivenessas an agent for catalyzing a glass slide for electrolessmetal deposition in less than three days even though the modifiedcomposition is boiled during its preparation.

EXAMPLE 8

In studying the effect of the ratio of monovalent copper to divalentcopperin material introduced in preparing the copper complexes, thefollowing substances are mixed together at room temperature until a darkcompositionis formed.

CuCl: 65 g.

CuCl₂.2H₂ : 200 g.

HCl: 500 ml.

Water sufficient for: 1 liter

Cu⁺ :Cu⁺⁺ ratio: 0.56:1

No precipitate resulted from the dropwise addition of thio solution towater. A more sensitive test was employed to verify the existence of anactivatable copper complex. A clean glass slide was immersed in thesolution for 1 minute and then submerged in water. The formation of someprecipitate as a hazy coating on the surface of the slide indicated thatthe desired complex was present.

EXAMPLE 9

A solution is formed in exactly the same manner as in Example 8 exceptfor increasing the amount of CuCl charged from 65 to 200 g. with acorresponding increase in the atomic ratio of monovalent copper todivalent copper to 1.72:1. The resulting product is a dark compositionandit yields a heavy precipitate upon dropwise addition to water.

EXAMPLE 10

The procedure of Example 8 is again repeated with a composition whichdiffers only in that the amount of CuCl charged is now increased from 65to about 400 g., and this results in a solution saturated with thatsalt, for an estimated 100 g. of the cuprous salt remains undissolvedeven afterthorough agitation of the mixture. The ratio of monovalentcopper in solution to divalent copper therein is estimated to be about2.6:1. Upon testing the resulting dark complex by adding it dropwise towater, a very thick precipitate is formed, considerably heavier thanthat of Example 9.

Upon comparing the results of Examples 8, 9 and 10, it is evident that ahigh atomic or weight ratio of monovalent copper to divalent copper isimportant in providing a high yield of the copper complex.

EXAMPLE 11

Other batches of the complex of Example 1 are prepared and the liquid isseparated from the metallic copper; then barium chloride is added to thecompositions in several amounts ranging from about 40 to about 200 g./l.It is found that this additive substantially increases the shelf life orstability in storage of the specimens of copper complex withoutaffecting their activity. However, for prolonged storage, oxidationeventually occurs unless the composition is maintained in contact withmetallic copper and there are periodic additions of hydrochloric acidand water to compensate for evaporation. Such oxidation is undesirableas it causes at least part of the copper complex to decompose with aconsequent loss of the property of precipitating upon addition to water.There is reason to believe that the complex composition may bemaintained in stable conditionover an indefinite period if it is kept ina sealed container with copper metal present therein.

EXAMPLE 12

Example 11 is repeated with cobaltous chloride employed as a stabilizerin lieu of the barium chloride and in the same proportions. The resultsobtained with this cobalt compound are similar in providing improvedstorage stability without the loss of activity of the complexcomposition in the absence of metallic copper for a reasonable length oftime, but prolonged storage requires measures along the lines suggestedin Example 11.

EXAMPLE 13

In another method for preparing the copper complex by the oxidation of areagent grade cuprous halide, the following substances are broughttogether:

CuCl (reagent grade): 70 g.

HCl: 200 ml.

Water sufficient for: 1 liter

Copper metal sheet: 500 cm.²

This composition is heated at 40° to 45° C. and passed over the coppersheets until a dark complex forms.

Initially the composition is colorless but it eventually turns very darkover a period of several days, and reaches an equilibrium as long as thehydrochloric acid concentration and the presence of copper metal aremaintained.

EXAMPLE 14

A composition having the components and proportions of Example 13 isoxidized by bubbling air through the solution in the presence of coppermetal and a dark complex is formed more rapidly than before.

EXAMPLE 15

A further method of forming the said complexes of this inventioninvolves essentially reduction in converting part of a divalent coppercompound to a monovalent form by making up the following composition:

CuCl₂.2H₂ O: 121 g.

HCl: 200 ml.

Water sufficient for: 1 liter

Copper chips: 30 g.

The above solution is agitated in the presence of the copper metal untila dark complex forms. This conversion occurs rapidly, especially whenthe composition is heated somewhat above 40° C.

EXAMPLE 16

The complex compositions of Examples 1 to 7 and 11 to 15 are eachemployed separately in treating a laminate for electroless copperdeposition according to the following processing sequence.

1. A phenolic paper laminate coated with a rubber-phenolic resinadhesive is preliminarily treated by immersion for 15 minutes at 35° to45° C. in a solution of the following composition:

CrO₃ : 100 g. H₂ SO₄ : 300 ml.

Surfactant FC-98: 0.5 g.

Water sufficient for: 1 liter

2. The substrate is neutralized in a bath containing 100 ml. of 85%hydrazine hydrate and 50 g. of sodium hydroxide per liter of water for 3to 4 minutes.

3. The neutralized substrate is now rinsed in tap water for about 1.5minutes.

4. Each laminate is now immersed in one of the complex seedercompositions of one of the aforesaid examples for a period from 10 to 15minutes with constant and thorough agitation in the composition.

5. Upon removal from the seeder composition, each laminate is subjectedto a rinse in running tap water for a period of about 45 to 75 secondsto convert the complex on the substrate to an adherent deposit of awater insoluble nature.

6. Next, the activity of the substrate is enhanced by reduction for 7 to10minutes in an alkaline sodium borohydride solution containing 1 g. ofNaBH₄ and 2 ml. of 50% aqueous sodium hydroxide per liter of water(pH≈12.3).

7. Reduction is followed by a rinse for 5 minutes in water.

8. The sensitized substrate is then subjected to electroless copperplatingby immersion for 30 to 45 minutes with thorough agitation in anelectrolesscopper deposition bath of the formula:

CuSO₄.5H₂ O: 30 g./l.

Rochelle Salts: 150 g./l.

Sodium Cyanide: 30 mg./l.

Formaldehyde (37% aqueous): 15 ml./l.

Wetting agent: 1 ml./l.

Sodium Hydroxide to: pH 13

Water to volume:

Electroless copper is deposited in a layer of the desired thickness oneachof the substrates treated with the complexes of Examples 1 to 7 and11 to 15. After thorough rinsing in water, each of these specimensdisplays a good peel strength indicative of firm bonding of theelectroless copper tothe substrate.

EXAMPLE 17

In a somewhat similar procedure as that of Example 16, additionalsamples of the same adhesive-coated phenolic laminate are subjected tosteps 1 to 5, inclusive, of Example 16, in the same manner as in theaforementioned process, with each laminate specimen being treated with adifferent complex seeder composition as before, but the subsequentprocessing is different and simpler than the previous steps designatedas 6, 7 and 8. Inthe instant embodiment each laminate is immersed for 45minutes in a simplesolution of an electroless metal containing a strongreducing agent in the form of an amineborane. Such a reducing compoundnot only serves its usualfunction in the deposition bath but alsosubstantially enhances the catalytic activity of the water-insolublederivative coating on the laminate. In illustration of the deposition ofanother metal, nickel, the electroless metal solution has the followingcomposition:

NiSO₄.6H₂ O: 8 g.

Dimethylamine borane: 1.35 g.

Formaldehyde (37%): 2.5 ml.

Monoethanolamine: 40 ml.

2-mecaptobenzothiazole: 0.5 mg.

Water to make: 1000 ml.

pH: 12.5 ml.

After the customary washing in water, it is found that the electrolessnickel is firmly bonded to all laminate specimens. Such surfaces may beplated up further with additional amounts of the same metal or withdifferent metals, such as copper, cobalt, silver, gold and the like.

EXAMPLE 18

Another copper complex is prepared and stabilized by the reductionmethod with the following materials:

CuCl (technical grade)*: 80 g.

NCl: 300 ml.

Surfactant FC:98: 0.5 g.

Water sufficient for: 1 liter

Copper metal sheet: 500 cm.²

When a dark complex appears, it is employed for treating two specimens,onebeing a clean glass slide and the other a laminate coated with anadhesive of the type mentioned hereinbefore and pretreated as describedin steps 1 to 3 of the foregoing processing sequence. Each of thesespecimens is immersed for 5 minutes in the treating composition of thisexample while thorough agitation is maintained, then rinsed for 5minutes in running water. Upon immersion of these specimens in a roomtemperature electrolesscopper deposition bath of the aforementionedcomposition while adequate agitation is maintained, it is observed thatafter 15 minutes in the bath,electroless copper begins to appear on thelaminate, and the latter is 99% covered at the end of 1 hour.

This embodiment of the instant process is simpler in employing noreducing agent step following sensitising.

EXAMPLE 19

In a preparation employing cobalt rather than copper in elemental form,thefollowing constituents are stirred together until the liquid turnsdark with the formation of a complex:

CuCl₂.2H₂ O: 120 g.

HCl: 200 ml.

Cobalt metal dust: excess

Water sufficient for: 1 liter

EXAMPLE 20

A mixture of:

CuCl₂.2H₂ O: 120 g.

HCl: 300 ml.

Iron dust: excess

Water sufficient for: 1 liter

is stirred until a dark complex is formed, and an exotherm is observedduring this procedure. Aluminum dust can be substituted withsubstantiallythe same results.

EXAMPLE 21

A mixture of metal salts is illustrated in the following compositionwhich is shaken until a dark complex appears.

CoCl₂.6H₂ O: 120 g.

CuCl₂.2H₂ O: 120 g.

HCl: 200 ml.

Copper dust: excess

Water sufficient: 1 liter

EXAMPLE 22

A variation of the formulation in Example 19 is prepared with 120 g. ofNiCl₂.6H₂ O substituted for the cobalt salt, and a dark complex isformed while the mixture is being shaken.

EXAMPLE 23

When carefully cleaned laminate samples are immersed separately in eachof the compositions of Examples 18 to 22, and then rinsed in water, awater insoluble deposit is observed on the surfaces of each of the testlaminates. Further processing of the treated laminate by reduction andelectroless plating as described hereinbefore demonstrates theoccurrence of substantial catalytic activation of the laminate surfaces.

EXAMPLE 24

The following solution was prepared at room temperature:

CuCl (technical grade): 200 g.

HCl: 550 ml.

FC:98: 0.1 g.

Water sufficient for: 1 liter

Copper metal sheet: 250 cm²

Epoxy/glass laminates coated with a rubber-base resinous adhesive(Beiersdorf Technicoll 801) were rendered hydrophilic in achrome/sulfuricactivating solution comprising 100 grams/liter CrO₃ and350 milliliters/liter 98% sulfuric acid and immersed in a liquid seedingmedium formed from the above solution, with all other preceding andsubsequent steps and conditions being according to Example 16. Theseedingand metallizing process was carried out until the seedingliquid's strengthhad been reduced enough to result in sporadicelectroless copper plating onthe substrate surface. It was determinedthat one gallon of the seeder liquid of this example was capable ofseeding about 300 square feet of substrate of the sort described withoutreplenishment of the seeder liquidin any way, including additional CuClor elemental copper.

While the present invention has been described in full detail in respecttoa limited number of examples for the purposes of complete disclosure,it will be appreciated by those skilled in the art that many othermodifications and embodiments fall within the purview of this invention.

We claim:
 1. A process for the electroless deposition of metal on anon-metallic surface, said process comprising the steps of:(a)pre-sensitizing the non-metallic surface to the electroless depositionof metal by contacting said non-metallic surface with a liquid mediumcomprising an admixture of a polar liquid, a halide, cupric ions andcuprous ions in a weight ratio of cuprous ions to cupric ions of atleast 0.4:1; (b) Rinsing said contacted surface with an aqueous solutionand forming an adherent water-insoluble derivative of said liquid mediumadsorbed on said non-metallic surface; (c) treating said rinsed surfacewith an electroless metal deposition bath containing a reducing agent torender said insoluble derivative catalytic to the electroless depositionof metal; and (d) contacting said catalytically sensitive surface withan electroless metal deposition bath to form an electroless deposit ofmetal thereon.
 2. A process according to claim 1, wherein said reducingagent includes at least one member selected from the group consisting ofborohydrides, amine boranes and hydrazine hydrate.
 3. A processaccording to claim 1, wherein said liquid medium also contains astabilizer.
 4. A process according to claim 1, wherein said liquidmedium also contains a wetting agent.